Multi-fuel fired vapor generating unit



Dec. 19, 1961 c.- B. BAVER MULTI-FUEL FIRED VAPOR GENERATING UNIT Filed Sept. 29, 1955 2 Sheets-Sheet 1 INVENTOR.

CLYDE B. BAVER ATTORNEY Dec. 19, 1961 c. B. BAVER MULTI-F'UEL FIRED VAPOR GENERATING UNIT Filed Sept. 29, 1955 2 Sheets-Sheet 2 FIG.2

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70 8O '90 OF MAXIMUM BOILER STEAM FLOW INVENTOR.

CLYDE B. BAVER ATTORNEY ate iv The present invention relates to the construction and operation of vapor generating and superheating units designed to be fired by multiple fuels, and more par ticularly to the construction and operation of such units for maintaining a predetermined substantially constant vapor superhcat temperature throughout a wide load range when the fuels are fired either singly or in combination.

In the steel industry, for example, the process of making steel creates relatively low heat value by-product fuels, such as blast furnace gas and coke oven gas. The increasing cost of relatively rich prime fuels such as oil and coal, makes eflicient utilization of such by-product fuels mandatory for most steel plants. The economical use of these by-product fuels singly and in combination is a major factor affecting the development of steam generating equipment suitable for steel mills. However, the demand for steam in most steel mills is usually more consistent than the supply of by-product fuels, requiring that such fuels be burned in combination with a prime fuel when the supply of by-product gas is low, or that a prime fuel alone be burned when no by-product gas is available.

The firing of blast furnace or coke oven gas results in the generation of heating gases which are about double in volume to those generated when burning pulverized coal or oil for the same steam output of the unit. For this reason the gas flow areas of such a gas burning unit must be designed to avoid excessive draft loss. This factor is also of importance in regard to the steam superheat temperature attainable. As is well known, a superheater of the radiant type, i.e. heated predominantly by radiation, has the characteristic of a rising steam temperature as load decreases. A convection superheater, on the other hand, has the characteristic of a decreasing steam temperature with load decrease. Consequently if blast furnace gas and oil should be separately and similarly fired for the same steam load on a unit in which the steam is superheated by convection, the greater volume of heating gases produced with blast furnace gas will result in substantially higher steam superheat temperatures throughout the load range. Variation in steam superheat temperatures is highly undesirable from the standpoint of efficiency of the steam utilizing equipment, such as a steam turbine.

In accordance with the present invention, a vapor generating and superheating unit of this type is provided with a vapor superheater constructed and arranged to receive heat partly by convection and partly by radiation in combination with a multi-fuel burner arrangement in which some or all of the burners for firing a prime or rich fuel, such as oil or pulverized coal, are positioned nearer to the combination radiant-convection superheater than the burners for firing byproduct gas, so as to secure an increased radiant and convection heating effect on the superheater when burning a prime fuel.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

3,013,549 Patented Dec. 19, 1961 Of the drawings:

FIG. 1 is a sectional elevation of the main portion of a steam generating and superheating unit constructed in accordance with the invention;

FIG. 2 is an enlarged sectional elevation of one of the combination oil and blast furnace gas burners shown in PEG. 1; and

1G. 3 is a graph showing a comparison between the superheat temperatures attainable with the use of the present invention and a similar type unit with a convection superheater and a burner arrangement as heretofore used.

The steam generating and superheating unit illustrated in FIGS. 1 and 2 comprises a vertically elongated furnace chamber 10, the sides of which are defined by a vertical front wall 11, opposite vertical side walls 12, and a shorter vertical rear wall 13. The lower end of the furnace chamber is formed by a water cooled ash hopper 1d and the upper end closed by a roof 15. The rear wall 13 terminates short of the roof 15 and the space therebetweeh defines a rectangular furnace chamber heating gas outlet 16. A double bank of vertically arranged steam generating tubes 23 is positioned in and rearwardly of the heating gas outlet 15 and connected at their lower and upper ends to a lower water drum 2i) and an upper steam and water drum 22. To reduce the gas pressure drop, the tube banks 23 are free of baffles provid ing a single pass heating gas flow across the tube banks. The front, rear and side Walls of the furnace chamber are lined with vertical steam generating tubes 25, these tubes receiving a water supply from the Water drum 20 and discharging the steam generated through suitable headers and connecting tubes to the steam and water drum 22. The tubes 25 lining the rear wall 13 are continued upwardly beyond that wall to form a slag screen 26 in front of the tube banks 23.

In accordance with the present invention, a steam superheater formed by transversely spaced platens of nested multiple looped superheater tubes 3%, with their ends connected to superheater inlet and outlet headers 31 and 32 respectively carried by the supporting steel work, is positioned in front of the steam generating tube banks 23 and slag screen 26 in the upper portion of the furnace chamber. The superheater tubes extend downwardly adjacent the slag screen and are bent at an angle rearwardly and terminate adjacent the rear wall 13 at a level below the level of the water drum 20. With this arrangement the superheater tubes will be heated partly by radiation from the fuel burning in the furnace chamber and partly by convection from the heating gases flowing contact therewith before the gases reach the heating gas outlet 16. This combination of radiant and convection heating of the superheater tubes will result in a substantially flatter superheat temperature curve over the load range compared to that of a convection superheater located within the tube banks 23 or between the tube banks 23 and slag screen 26.

Also, in accordance with the invention, the steam generating and superheating unit described is arranged to be fired by both a prime fuel, oil, and a by-product gas, blast furnace gas, either singly or in combination. For this purpose the unit is provided with upper and lower rows of combination oil and gas burners 40 and 41 respectively horizontally arranged in the front wall 11 at levels below the lowermost end of the superheater tubes 3d. As shown in FIGS. 1 and 2, the combination fuel burners are arranged to fire through burner ports 42 in the front wall to which combustion air is delivered from a windbox 43 along the front wall 11. Each of these fuel burners has a horizontally arranged fuel gas duct 44 having a tangentially arranged scroll inlet 45 at its outer end and circular series of external and internal auras-so deflecting blades 46 at its inner end for effecting a whirl in the discharging gas and combustion air streams entering the burner port 42 to promote mixing therebetween. The resulting flame is relatively short and turbulent and extremely stable. An oil atcmizing nozzle 47 is arranged axially of the gas duct 44 and projects through opposite ends thereof. The supply of combustion air to each burner port is controlled by manually operated dampers 43.

A row of burner ports 50 is located in the front wall 11 above the level of the upper row of combination fuel burners 40 and arranged to receive a controllable supply of combustion air from the windbox 43. A horizontally positioned oil atomizing nozzle 52 carrying an impeller cone 53 on its inner end is axially aligned with each burner port 50. As so arranged the oil burners will be approximately opposite the lower end portion of the superheater tubes. With this location the oil burners will be a shorter distance in the furnace from the superheater tubes and this coupled with the high flame temperature of the burning oil insures a substantial radiant heating of the superheater tubes when the oil burners 52 are in use. Also this oil burner location insures a relatively short travel of the heating gases generated in the furnace before reaching the superheater tubes and thus correspondingly reduces the cooling eifect on these gases of the furnace chamber wall tubes 25. These gases will thus have a higher temperature on reaching the superheater tubes than those from the subjacent combination fuel burners 40, 41, when burning gas or oil singly or in combination.

The steam generating unit illustrated is designed for a steam generating capacity of 250,000 lbs. of steam per hour at 675 p.s.i.g. when firing either oil or blast furnace gas. A superheat temperature of 840 F. is obtained at full capacity with either fuel. When burning oil alone, it is preferable that only the two upper rows of oil burners 47 and 52 be operated, thus decreasing the furnace heat absorption and making more heat available to the superheater. When burning blast furnace gas, the two rows of gas burners are operated. The substantially greater volume of heating gases, although lower flame temperature, of the burning gas permits a longer gas travel in the furnace chamber before reaching the superheater and substantially the same total radiation and convection superheating effect as with oil.

in FIG. 3, curves A and B represent the superheat temperature conditions in a unit similar to that illustrated except for the location of all of the steam superheating surface between the slag screen and generating tube bank and the oil and blast furnace gas burners at the same two levels. Curve A illustrates the superheat temperature variations in such a unit when burning oil alone, while curve B illustrates the superheat temperatures when burning blast furnace gas alone. In both cases the temperatures vary considerably over the normal load range of 40l00%, with substantially the same relatively wide difference in maximum steam temperatures attainable over this load range. Curve C indicates the superheat temperature conditions attainable with the unit illustrated in FIGS. 1 and 2 when burning blast furnace gas alone, while curve D shows the superheat temperature variations in that unit when burning oil alone in the two upper rows of oil burners. The curves C and D are relatively fiat throughout the normal load range and the steam temperature differences between the use of the two fuels has been greatly reduced, permitting the associated steam utilizing equipment to operate at its est efficiency.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and

. 4- that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

Iclaim:

l. A multiple fuel fired vapor generating and superheating unit comprising vertical walls defining a vertically elongated furnace chamber having a heating gas outlet in its upper portion, a bank of vertically arranged vapor generating tubes arranged to receive heating gases from said furnace chamber outlet, a vapor superheater comprising groups of vertically arranged vapor superheating tubes in the upper portion of said furnace chamber arranged at the furnace side of and adjacent to said vapor generating tube bank, said vapor superheating tubes being arranged to receive heat partly by convection and partly by radiation, means for firing said furnace chamber comprising a row of horizontally directed fuel gas burners positioned in one of said walls below the level of said tube bank and a row of horizontally directed burners for burning a relatively rich fuel in suspension positioned in said last named wall above the row of gas burners, and means for separately supplying a low heat value gas to said gas burners and a rich fuel to said rich fuel burners.

2. A multiple fuel fired vapor generating and superheating unit comprising vertical front, rear and side walls defining a vertically elongated furnace chamber having a heating gas outlet in its upper rear wall, a bank of vertically arranged vapor generating tubes arranged to receive heating gases from said furnace chamber outlet, a vapor superheater comprising groups of vertically arranged vapor superheating tubes in the upper portion of said furnace chamber arranged in front of and adjacent to said vapor generating tube bank, said vapor superheating tubes being arranged to receive heat partly by convection and partly by radiation, means for firing said furnace chamber comprising a row of horizontally directed fuel gas burners positioned in said front wall below the level of said tube bank and a row of horizontally directed burners for burning a relatively rich fuel in suspension positioned in said front wall above the row of gas burners, and means for separately supplying a low heat value gas to said gas burners and a rich fuel to said rich fuel burners.

3. A multiple fuel fired vapor generating and superheating unit comprising vertical front, rear and side walls defining a vertically elongated furnace chamber having a heating gas outlet in its upper rear wall, vapor generating tubes lining said walls substantially throughout their height, a bank of vertically arranged vapor generating tubes arranged to receive heating gases from said furnace chamber outlet, a vapor superheater comprising groups of vertically arranged vapor superheating tubes in the upper portion of said furnace charnber arranged in front of and adjacent to said vapor generating tube bank and extending downwardly below the lower end of said tube bank, said vapor superheating tubes being arranged to receive heat partly by convection and partly by radiation, means for firing said furnace chamber comprising a row of horizontally directed fuel gas burners positioned in said front wall below the level of said tube bank and a row of horizontally directed burners for burning a relatively rich fuel in suspension positioned in said front wall above the row of gas burners, and means for separately supplying a low heat value gas to said gas burners and a rich fuel to said rich fuel burners.

4. A multiple fuel fired vapor generating and superheating unit comprising vertical front, rear and side walls defining a vertically elongated furnace chamber having a heating gas outlet in its upper rear wall, vapor generating tubes lining said walls substantially throughout their height, a bank of vertically arranged vapor generating tubes arranged to receive heating gases from said furnace chamber outlet, a vapor superheater comprising groups of vertically arranged vapor superheating tubes in the upper portion of said furnace chamber arranged in front of and adjacent to said vapor generating tube bank and extending downwardly below the lower end of said tube bank, said vapor superheating tubes being arranged to receive heat partly by convection and partly by radiation, means for firing said furnace chamber comprising rows of horizontally directed fuel gas burners positioned at a plurality of levels in said front wall below the level of said tube bank and a row of horizontally directed burners for burning a relatively rich fuel in suspension positioned in said front wall above the uppermost row of gas burners and opposite the lower end of said vapor superheating tubes, and means for separately supplying a low heat value gas to said gas burners and a rich fuel to said rich fuel burners.

5. The method of operating a vapor generating and superheating unit having a vertically elongated fluid cooled furnace chamber, a bank of vapor generating tubes arranged to receive heating gases from-the upper portion of said furnace chamber, and vapor superheating tubes in the upper portion of said furnace chamber at the furnace chamber side of and adjacent to said generating tube bank, said vapor superheating tubes being arranged to receive heat partly by convection and partly by radiation, which comprises firing said furnace chamber with a low heat value fuel gas introduced at a level below said generating tube bank when said fuel gas is available, and firing said furnace chamber at the other times with a relatively rich fuel introduced and burning at least in part at a level above the combustion level of said gas to maintain substantially constant steam superheat temperature values under both fir ing conditions.

6. The method of operating a vapor generating and superheating unit having a vertically elongated fluid cooled furnace chamber, a bank of vapor generating tubes arranged to receive heating gases from the upper portion of said furnace chamber, and vapor superheating tubes in the upper portion of said furnace chamber at the furnace chamber side of and adjacent to said generating tube bank, said vapor superheating tubes being arranged to receive heat partly by convection and partly by radiation, which comprises firing said furnace chamber with a low heat value fuel gas introduced at a level below said generating tube bank and at rates sufficient to maintain a substantially constant superheat temperature over a relatively wide load range, and firing said furnace chamber at other times with a relatively rich fuel introduced and burning at least in part at a level above the combustion level of said gas and at rates sufiicient to maintain superheat temperature values similar to those obtained when firing said unit with gas.

References Cited in the file of this patent UNITED STATES PATENTS 1,517,291 Jacobus Dec. 2, 1924 2,143,820 Payn Jan. 10, 1939 2,367,193 Blizard Jan. 16, 1945 2,685,279 Caracristi Aug. 3, 1954 2,699,761 Rehm Jan. 18, 1955 FOREIGN PATENTS 428,880 Germany May 12, 1926 

